Dried, singulated cellulose pulp fibers are desirable for many products from absorbent personal articles to a strengthener in concrete. Currently, in the most common process of making singulated fibers, a roll of conventional pulp fibers is hammermilled into singulated fibers. This process is energy-intensive, requiring an additional drying stage. Further, the current hammermilling process often produces fibers with undesirable physical properties, such as low kink, curl, and twist.
This dried, singulated pulp will also contain knots of fiber, sometimes referred to as nits or nodules. Knots are fiber clumps that remain strongly adhered to one another, as can be seen by placing a small portion of pulp into a clear beaker of water and stirring the water to mix the fibers. Most of the fiber will mix into the water as singular fibers; however, there will be fiber clumps that are readily visible. The fiber clumps or knots are undesirable by-products of the hammermilling process. The amount of knots in a pulp that has been hammermilled can be quantified by using a screening system with acoustical energy used as the means to classify the fiber into sizes of knots, accepts, and fines. It is desirable to have low knots and fines and high accepts where the accepts are the singulated fibers.
Canadian Patent No. 993618 (Estes, 1976) describes a process for producing a low density fluff pad or batt from individual fibers that have significant kink and interlocking to provide improved batt strength and higher bulk. In accordance with the process, wet pulp is separated into individual fibers during the drying stage. The process uses fluid jet drying equipment that employs air-jets or steam-jets for separating the fibers. The fibers are laid on a perforated screen upon exiting from the jet dryer. The fibers produced from this reference were dried at a temperature of 204° C. with no mention of knots. At that temperature, the throughput will be uneconomically low. United States Patent Publication No. US 2003/0182818 A1 describes a process for producing individual fibers utilizing a jet dryer. This publication suggests the use of steam injected into the jet dryer to reduce the numbers of knots in the resulting fiber. It has been found that the injection of steam does reduce the number of knots or nits in the final fiber.